The overall or long range interest in the project is concerned with the role that macrophages might have in bone resorption. The experimentation involves in vitro cell and organ culture techniques utilizing peritoneal macrophages and newborn mice calvaria. This particular project involves the response that macrophages might have to know in vivo modulators of bone resorption (e.g., parathyroid hormone (PTH), 1,25 dihydroxycholecalciferol (DHCC), or calcitonin (CT). Acid phosphatase and the release of previously incorporated 45 Calcium (both indicators of in vivo bone resorption) will be measured in the following 4 types of culture; peritoneal macrophages cultured alone, p. macrophages cultured with newborn mouse calvaria, or newborn calvaria cultured alone, or purified fibroblasts grown with newborn calvaria. Each of these four cultures will be treated with each of the above three hormones. An ultrastructural comparison (SEM & TEM) between the macrophages of these cultures and bone resorbing osteoclasts will also be made. The second phase of this research project involves studies concerned with the chemotaxic responses that macrophages might have to various prepared bone matrices. Matrices will be prepared by separation into different components and treatment with bone modulators (e.g., PTH, l, 25 DHCC and/or calcitonin). These matrices will then each be tested for chemotactic responses to macrophages.